The invention relates to novel methods, compositions, and apparatuses for improving the effectiveness of froth flotation beneficiation processes. In a beneficiation process, two or more materials which coexist in a mixture (the fines) are separated from each other using chemical and/or mechanical processes. Often one of the materials the beneficiary) is more valuable or desired than the other material (the gangue).
As described for example in U.S. Pat. Nos. 4,756,823, 5,304,317, 5,379,902, 7,553,984, 6,827,220, 8,093,303, 8,123,042, and in Published US Patent Applications 2010/0181520 A1 and 2011/0198296, and U.S. patent application Ser. No. 13/687,042, one form of beneficiation is froth flotation separation. Commonly, flotation uses the difference in the hydrophobicity of the respective components. The components are introduced into the flotation apparatus sparged with air, to form bubbles. The hydrophobic particles preferentially attach to the bubbles, buoying them to the top of the apparatus. The floated particles (the concentrate) are collected, dewatered and accumulated. The less hydrophobic particles (the tailings) tend to migrate to the bottom of the apparatus from where they can be removed.
Two common forms of flotation separation processes are direct flotation and reverse flotation. In direct flotation processes, the concentrate is the beneficiary and the tailings are the gangue. In reverse flotation processes, the gangue constituent is floated into the concentrate and the beneficiary remains behind in the slurry. The object of flotation is to separate and recover as much of the valuable constituent(s) of the fine as possible in as high a concentration as possible which is then made available for further downstream processing steps.
Froth flotation separation can be used to separate solids from solids (such as the constituents of mine ore) or liquids from solids or from other liquids (such as the separation of bitumen from oil sands). When used on solids, froth separation also often includes having the solids comminuted (ground up by such techniques as dry-grinding, wet-grinding, and the like). After the solids have been comminuted they are more readily dispersed in the slurry and the small solid hydrophobic particles can more readily adhere to the sparge bubbles.
There are a number of additives that can he added to increase the efficiency of a froth flotation separation. Collectors are additives which adhere to the surface of concentrate particles and enhance their overall hydrophobicity. Gas bubbles then preferentially adhere to the hydrophobized concentrate and it is more readily removed from the slurry than are other constituents, which are less hydrophobic or are hydrophilic. As a result, the collector efficiently pulls particular constituents out of the slurry while the remaining tailings which are not modified by the collector, remain in the slurry. Examples of collectors include oily products such as fuel oil, tar oil, animal oil, vegetable oil, fatty acids, fatty amines, and hydrophobic polymers. Other additives include frothing agents, promoters, regulators, modifiers, depressors (deactivators) and/or activators, which enhance the selectivity of the flotation step and facilitate the removal of the concentrate from the slurry.
The performance of collectors can be enhanced by the use of modifiers. Modifiers may either increase the adsorption of collector onto a given mineral (promoters), or prevent collector from adsorbing onto a mineral (depressants). Promoters are a wide variety of chemicals which in one or more ways enhance the effectiveness of collectors. One way promoters work is by enhancing the dispersion of the collector within the slurry. Another way is by increasing the adhesive force between the concentrate and the bubbles. A third way is by increasing the selectivity of what adheres to the bubbles. This can be achieved by increasing the hydrophilic properties of materials selected to remain within the Shiny, these are commonly referred to as depressants.
Frothing agents or frothers are chemicals added to the process which have the ability to change the surface tension of a liquid such that the properties of the sparging bubbles are modified. Frothers may act to stabilize air bubbles so that they will remain well-dispersed in slurry, and will form a stable froth layer that can be removed before the bubbles burst. Ideally the Bother should not enhance the flotation of unwanted material and the froth should have the tendency to break down when removed from the flotation apparatus. Collectors are typically added before frothers and they both need to be such that they do not chemically interfere with each other. Commonly used frothers include pine oil, aliphatic alcohols such as MIBC (methyl isobutyl carbinol), polyglycols, polygloycol ethers, polypropylene glycol ethers, polyoxyparafins, cresylic acid (Xylenol), commercially available alcohol blends such as those produced from the production of 2-ethylhexanol and any combination thereof.
Because collectors adhere to the surfaces of concentrate particles, their effectiveness is dependent on the nature of the interactions that occur between the collectors and the concentrate particles. Unfortunately contradictory principles of chemistry are at work in froth flotation separation which forces difficulties on such interactions. Because froth flotation separation relies on separation between more hydrophobic and more hydrophilic particles, the slurry medium often includes water. Because however many commonly used collectors are themselves hydrophobic, they do not disperse well in water which makes their interactions with concentrate particles difficult or less than optimal.
One method that has been used to better disperse water immiscible collectors in slurry is through the use of chemical agents such as emulsifiers to disperse is the collector in the slurry as an oil-in water type emulsion. Unfortunately here too contradictory chemistry has hampered this attempt. To make oil-in-water emulsions stable sufficient amounts of emulsifiers have to be used to cover the surface of oil droplets with a hydrophobic tail portion and the water phase with a hydrophilic group. However, when used in these amounts emulsifiers reduce the hydrophobicity of the collector thus defeating the entire purpose of being a collector. As a result water immiscible collector performance remains degraded because of either poor dispersing or because of impaired hydrophobicity. In addition using sufficient emulsifiers to disperse collectors often causes interferes with other additives (frothing agents in particular).
Thus it is clear that there is definite utility in improved methods, compositions, and apparatuses for applying collectors in froth separation slurry. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.